Method of formation testing

Abstract

A new technique for interpreting pressure data measured during a formation test. The new technique uses an exact spherical flow model that considers the effects of flow line storage and that can be solved in closed, analytical form. This technique generates a type-curve that matches the entire measured pressure plot and that can accurately predict ultimate formation pressure during formation testing from a pressure plot that has not achieved steady state values near the formation pressure.

What is claimed is: 
     
       1. A method of testing an underground formation, said method comprising the steps of: disposing a formation testing device within a borehole adjacent a portion of said underground formation to be tested, said formation testing device having a probe for collecting fluid from said formation and having a transducer for measuring fluid pressure, said transducer being fluidically coupled to said probe by a flow line;   drawing fluid from said underground formation through said probe and into said formation testing device, and permitting fluid pressure within said formation testing device to build toward fluid pressure within said underground formation;   delivering an electrical signal from said transducer to a signal processor electrically coupled to said formation testing device, said electrical signal being correlative to fluid pressure of said fluid in said formation testing device;   generating an electrical plot in response to receiving said electrical signal, said electrical plot being correlative to fluid pressure of said fluid in said formation testing device over time; and   generating an electrical type-curve that approximates said electrical plot wherein said step of generating an electrical type curve comprises the steps of: delivering signals R w , V, Q 0 , μ, and φ, corresponding to radius of said borehole, volume of said flowline, rate of fluid flow into said formation testing device, viscosity of said fluid, and porosity of said formation, respectively to said signal processor;   determining compressibility of said fluid, and delivering electrical signals C and c correlative thereto;   estimating permeability of said formation, and delivering an electrical signal k correlative thereto;   determining permeability of said formation and pressure of said formation by altering said electrical signals P, R w , V, Q 0 , μ, φ, C, c, and k according to: ##EQU36##     
     
     
       2. The method of claim 1, further comprising the step of displaying said electrical plot and said electrical type-curve on a monitor. 
     
     
       3. The method as set forth in claim 1, further comprising the step of terminating said testing of said underground formation when said electrical type-curve provides a substantially unchanging estimate of fluid pressure in said underground formation. 
     
     
       4. A method of testing an underground formation, said method comprising the steps of: disposing a formation testing device within a borehole adjacent a portion of said underground formation to be tested, said formation testing device having a probe for collecting fluid from said formation and having a transducer for measuring fluid pressure, said transducer being fluidically coupled to said probe by a flow line;   drawing fluid from said underground formation through said probe and into said formation testing device, and permitting fluid pressure within said formation testing device to build toward fluid pressure within said underground formation;   delivering an electrical signal from said transducer to a signal processor electrically coupled to said formation testing device, said electrical signal being correlative to fluid pressure of said fluid in said formation testing device;   generating an electrical plot in response to receiving said electrical signal, said electrical plot being correlative to fluid pressure of said fluid in said formation testing device over time; and   generating an electrical type-curve that approximates said electrical plot wherein said step of generating an electrical type curve comprises the steps of: delivering signals R w , V, Q 0 , μ, and φ, corresponding to radius of said borehole, volume of said flowline, rate of fluid flow into said formation testing device, viscosity of said fluid, and porosity of said formation, respectively to said signal processor;   determining compressibility of said fluid, and delivering electrical signals C and c correlative thereto;   estimating permeability of said formation, and delivering an electrical signal k correlative thereto;   determining permeability of said formation and pressure of said formation by altering said electrical signals P, R w , V, Q 0 , μ, φ, C, c, and k according to: ##EQU37##     
     
     
       5. A method of testing an underground formation, said method comprising the steps of: disposing a formation testing device within a borehole adjacent a portion of said underground formation to be tested, said formation testing device having a probe for collecting fluid from said formation and having a transducer for measuring fluid pressure, said transducer being fluidically coupled to said probe by a flow line;   drawing fluid from said underground formation through said probe and into said formation testing device, and permitting fluid pressure within said formation testing device to build toward fluid pressure within said underground formation;   delivering an electrical signal from said transducer to a signal processor electrically coupled to said formation testing device, said electrical signal being correlative to fluid pressure of said fluid in said formation testing device;   generating an electrical plot in response to receiving said electrical signal, said electrical plot being correlative to fluid pressure of said fluid in said formation testing device over time; and   generating an electrical type-curve that approximates said electrical plot wherein said step of generating an electrical type curve comprises the steps of: delivering signals R w , V, Q 0 , μ, and φ, corresponding to radius of said borehole, volume of said flowline, rate of fluid flow into said formation testing device, viscosity of said fluid, and porosity of said formation, respectively to said signal processor;   determining compressibility of said fluid, and delivering electrical signals C and c correlative thereto;   estimating permeability of said formation, and delivering an electrical signal k correlative thereto;   determining permeability of said formation and pressure of said formation by altering said electrical signals P, R w , V, Q 0 , μ, φ, C, c, and k according to: ##EQU38##     
     
     
       6. A method of interpreting formation pressure data P electrically recorded by a formation testing device within a borehole adjacent a portion of an underground formation, said formation testing device having a probe for collecting fluid from said formation and having a transducer for measuring fluid pressure, said transducer being fluidically coupled to said probe by a flow line, said method comprising the steps of: delivering said electrically recorded pressure data P versus time t to a signal processor;   delivering electrical signals R w , V, Q o , μ, and φ, corresponding to radius of said borehole, volume of said flow line, rate of fluid flow into said formation testing device, viscosity of said fluid, and porosity of said formation, respectively, to said signal processor;   said signal processor: determining compressibility of said fluid, and delivering electrical signals C and c correlative thereto;   estimating permeability of said formation, and delivering an electrical signal k correlative thereto;   determining permeability of said formation and pressure of said formation by altering said electrical signals P, R w , V, Q o , μ, φ, C, γ, and k according to: ##EQU39##     
     
     
       7. A method of testing an underground formation, said method comprising the steps of: drilling a borehole into said underground formation;   disposing a formation testing device within said borehole adjacent a portion of said underground formation to be tested, said formation testing device having a probe for collecting fluid from said formation and having a transducer for measuring fluid pressure, said transducer being fluidically coupled to said probe by a flow line;   drawing fluid from said underground formation through said probe and into said formation testing device;   delivering an electrical signal P from said transducer to a signal processor electrically coupled to said formation testing device, said electrical signal P being correlative to fluid pressure of said fluid in said formation testing device;   recording said electrical signal P over time t to generate an electrical plot being correlative to fluid pressure of said fluid in said formation testing device over time;   delivering electrical signals R w , V, Q o , μ, and φ, corresponding to radius of said borehole, volume of said flow line, rate of fluid flow into said formation testing device, viscosity of said fluid, and porosity of said formation, respectively, to said signal processor;   determining compressibility of said fluid, and delivering electrical signals C and c correlative thereto;   estimating permeability of said formation, and delivering an electrical signal k correlative thereto;   determining permeability of said formation and pressure of said formation by altering said electrical signals P, R w , V, Q o , μ, φ, C, and k according to: ##EQU40##